When two or more signal wires run in parallel they have the potential to interfere with each other through either capacitive or inductive coupling effects. In general, capacitance is a short distance effect that impacts only immediately neighboring wires, and several different tools automated circuit design tools have been developed to detect and measure the impact of capacitive coupling in a circuit. Unlike capacitance, induction is a relatively long distance effect, and is therefore harder to detect and analyze. Inductive coupling occurs when a change in current flow through one component or wire induces a current flow in another component or wire through a shared magnetic field. Its impact is not necessarily limited to immediately neighboring wires, and in fact can reach far across a particular chip or system.
In the design and layout of VLSI (Very Large Scale Integration) devices, which have many wires, inductive coupling is especially difficult to analyze and correct. As circuit designs become denser, the number of parallel wires (traces) increases, while the spacing between the wires decreases. Inductive coupling can become a particular problem when these dense, wide busses switch at or near the same time. Powerful enough inductive coupling can cause glitches in digital circuits when inadvertent state changes in a wire are caused by the induction induced by one or more other wires changing state.
Current methods of detecting and correcting inductive coupling effects typically rely on traditional method of inductor extraction and analysis through circuit simulation tools, such as SPICE (Simulation Program with Integrated Circuit Emphasis). This limits the technology to analysis of a small subset of the total number of signals on the VLSI device. An alternate approach using reluctors has also been developed, however, such approaches are also limited in capacity and typically lack full chip coverage. Such methods also require knowledge of an effected area, and are thus ineffective at detecting unknown problem areas in a design. In general, present methods of detecting and analyzing inductive coupling effects are limited to circuit densities on the order of thousands of wires. Such methods are totally inadequate for circuit densities on the order of millions or tens of millions of wires.